Chapter 3 Reproductive System A good insight into reproductive systems of crop species is necessary for a plant breeder for the following reasons. Plant breeding methodology differs for the most part according to the system of reproduction of a crop species.To determine the most appropriate methodology for a crop species precise knowledge of its reproductive system is therefore essential. A plant breeder is required to make artificial hybridization for genetic studies to elicit information regarding inheritance of specific traits and interspecies relationships and for transferring desired characters from one breeding material to another.Precise knowledge of floral structure,floral biology,sex expression,mode of natural pollination and extent of natural outcrossing,etc.for the crop species with which a plant breeder is working is thus essential. Precise knowledge of reproductive behavior is also needed to control pollination to avoid unwanted hybrids (outcrosses)both in breeding nurseries and in pure seed production for commercial purposes,and in the development of hybrid varieties and hybrid seed production. The possible range of reproductive systems in crop species is rather large.The reproductive systems of interest to a plant breeder are discussed below. 1.Sexual Reproduction The normal sexual life cycle of a plant is shown in Fig.4.1. Sporophyte-meiosis-Spore-Gametophyte-fertilization-Zygote-Seed with embryo 1)Autogamy (Self-pollinated,Self-fertilized Crop Species) Crop species in which the pollen of a flower usually pollinates the stigma of the same flower are grouped as self-pollinated crops.The extent of self-pollination varies in different crop species.The following sex expressions favour self-pollination. a)）Cleistogamy Refer to the condition wherein pollination takes place in unopened flowers,thus ensuring total self-pollination. b)Chasmogamy Refer to the condition wherein the flower opens only after pollination has taken place.Since the flower opens some outcrossing may take place,though the extent is usually very low. c)Floral Structure In many species,although pollination usually takes place after the flower opens, self-pollination is ensured by the floral structure.The following floral structures favour self-pollination: 1)Stigma may be closely surrounded by anthers,e.g.tomato,eggplant 2)Stamens and stigma are hidden by other floral organs,e.g.legumes. 3)Stigma becomes receptive and elongates through the staminal column,which ensures predominant self-pollination. As a rule,when the extent of natural cross-pollination in a crop species is less7 Chapter 3 Reproductive System A good insight into reproductive systems of crop species is necessary for a plant breeder for the following reasons. ◇Plant breeding methodology differs for the most part according to the system of reproduction of a crop species. To determine the most appropriate methodology for a crop species precise knowledge of its reproductive system is therefore essential. ◇A plant breeder is required to make artificial hybridization for genetic studies to elicit information regarding inheritance of specific traits and interspecies relationships and for transferring desired characters from one breeding material to another. Precise knowledge of floral structure, floral biology, sex expression, mode of natural pollination and extent of natural outcrossing, etc. for the crop species with which a plant breeder is working is thus essential. ◇Precise knowledge of reproductive behavior is also needed to control pollination to avoid unwanted hybrids (outcrosses) both in breeding nurseries and in pure seed production for commercial purposes, and in the development of hybrid varieties and hybrid seed production. The possible range of reproductive systems in crop species is rather large. The reproductive systems of interest to a plant breeder are discussed below. 1. Sexual Reproduction The normal sexual life cycle of a plant is shown in Fig.4.1. Sporophyte—meiosis—Spore—Gametophyte—fertilization—Zygote—Seed with embryo 1) Autogamy (Self-pollinated, Self-fertilized Crop Species) Crop species in which the pollen of a flower usually pollinates the stigma of the same flower are grouped as self-pollinated crops. The extent of self-pollination varies in different crop species. The following sex expressions favour self-pollination. a) Cleistogamy Refer to the condition wherein pollination takes place in unopened flowers, thus ensuring total self-pollination. b) Chasmogamy Refer to the condition wherein the flower opens only after pollination has taken place. Since the flower opens some outcrossing may take place,though the extent is usually very low. c) Floral Structure In many species, although pollination usually takes place after the flower opens, self-pollination is ensured by the floral structure. The following floral structures favour self-pollination: 1) Stigma may be closely surrounded by anthers,e.g. tomato, eggplant. 2)Stamens and stigma are hidden by other floral organs,e.g. legumes. 3)Stigma becomes receptive and elongates through the staminal column, which ensures predominant self-pollination. As a rule, when the extent of natural cross-pollination in a crop species is less